Photoelectric chorus effect generator



April 16, 1963 E. M. JoNEs PRoToELEcTRIc cRoRUs EFFECT GENERATOR 2 Sheets-Sheet 1 Filed Aug. 17, 1959 INVEN TOR. EDWARD M. JONES /Y I L 49% Arm/mns April 16, 1963 E. M. JONES PHOTOELECTRIC CHORUS EFFECT GENERATOR 2 Sheets-Sheet 2 bb mm.

Filed Aug. 17, 1959 3,086,122, PHUTELECTRC CHRUS EFFECT GENERTQR Edward M. Jones, Cincinnati, hio, assigner to The Baldwin Piano Company, Cincinnati, (Ehio, a corporation of @hin Filed Aug. 17, 1959, Ser. No. 834,327 lll Claims. (Cl. Z50-220) This application is related in subject matter to an application for United States patent filed in the name of William C. Wayne, Jr., Serial No. 631,650, tiled December 31, 1956, and entitled Audio Modulation System now United States Patent No. 3,004,460, which is assigned to the same assignee as the present application.

The present invention relates generally to systems for achieving an ensemble effect in music by processing a band of audio frequencies, and more particularly by translating the frequency spectrum representative of the music so that it is either sharp or flat in controllable degree, over its entire extent, and differently in different parts of the spectrum, and more particularly to systems for translating frequency spectra as a Whole in one sense or another, by means of modulators employing photo-sensitive resistors.

The traditional pipe organ consists of many ranks of pipes which are invariably somewhat out of tune. Certain ranks of pipes, referred to as celestes, are purposely detuned by a considerable amount to produce a rich ensemble effect in the composite tone, which is especially desirable for use in ecclesiastical music. l't is a primary feature of the present invention to provide a system for photo-electrically processing a musical frequency spectrum, from Whatever' source derived, and `more particularly a musical frequency spectrum deriving from an electronic organ, to achieve a processed frequency spectrum displaced from the original spectrum by a xed amount, or by multiple discrete amounts, to the end that eleste and chorus effects may be obtained.

Briefly describing the present invention as related to a specific embodiment thereof, a plurality of Wide band single side-band photo-electric modulators is employed, each of which continuously shifts the phase of a wide band audio spectrum in such sense as to introduce a continuously changing phase shift of the entire' spectrum in a given direction, which is equivalent to a frequency shift of the spectrum in a given sense, i.e., llat or sharp. Different octaves of the Wide band spectrum may be selected from the wide band outputs of several modulators, each providing a different frequency shift, by means of bandpass filters, and the filtered sub-bands may be then recombined either electrically or acoustically, or partly electrically and partly acoustically, to provide a processed wide band frequency spectrum.

More specifically describing a modulator according to the invention, from a Wide band audio spectrum are derived, by phase splitting, three spectra of identical frequency and amplitude content, corresponding frequencies of which are, however, displaced 120 in time phase. The phase split components of the original 4signal are amplitude modulated at a low frequency rate by means of photo-sensitive modulating elements, more specifically photo-resistors, which are subjected to three phase amplitude modulated light. Upon linear recombination of the amplitude modulated signals derivable from the photoresistors, a processed signal is obtained whose phase angle continuously changes in a given sense relative to the input phase as a xed reference value. By selecting the phase sequence of the light modulation applied to the photo-resistors to have one sequence, the processed output Will have a continuously varying phase shift in a positive or increasing sense, and `for the opposite phase sequence in a negative or decreasing sense, with contates @atene 3,086,l22 Patented Apr. 16, 1963 rice equent increase or decrease of the frequency of the modulated band, respectively.

lt is well known to modulate light by means of an opaque or transparent shaped track on a rotating disc, the modulated light being intercepted by a photocell, which provides amplitude varying output corresponding with the track shape. Devices of this kind may be utilized as signal generators or as variable impedances and may be utilized for modulating the amplitudes of signals supplied to the photocells or photo-resistors as a function of the amount of light falling thereon as the track moves past the photocell.

ln accordance With one aspect of the present invention, a rotating disc having thereon either opaque or transparent tracks is utilized to modulate light deriving from an unmodulated light source and proceeding to a plurality of photo-resistors, the arrangement of the tracks and the relative locations of the photo-resistors relative to the tracks being arranged to provide polyphase modulation of the resistances of the photo-resistors. An audio source which is to be processed is split into three phases, separated by and each of the phases is connected in series with one of the photo-resistors, which are in turn resistance modulated by the light passing through the rotating tracks in polyphase relation. The current flowing through the photo-resistors, is then representative, respectively, of three phase audio signals, amplitude modulated at 120 relative phases, according to the signal provided by the rotating tracks. The photo-resistors may be connected in parallel to a common load resistance, across which then appears a replica of the original audio spectrum, frequency shifted by an amount equal to the frequency of variation of resistance of any one of the photo-resistors, in response to rotation of the tracks.

ln accordance with a modification of the present invention elongated photo-resistors are employed, which are spaced about a circle at 120 intervals, the photo-resistors extending radially of the circle. An eccentrically mounted opaque disc is rotated adjacent to the photo-resistors, and is so located that light from a convenient source is caused to fall on varying lengths of the photo-resistors as the disc rotates. If the disc is circular and eccentrically rotated, the total area of any photocell which is exposed to the light varies sinusoidally. By locating the photoresistors at 120 intervals about the circle the illuminated areas of the several photo-resistors vary sinusoidally, but at 120 relative phase relation in the several photo-resistors. The resistance of any one photo-resistor varies in accordance with the total exposed area thereof, and accordingly varies sinusoidally, and the frequency of variation is equal to the frequency of rotation of the disc.

As in the previously described embodiment of the present invention, a source of audio signals, deriving from an electronic organ or from any other convenient source, may be phase split into three spectra phase separated by 120, and the several phase split spectra may be modulated by several modulators of the character above described, each employing a disc rotating at a different frequency. Sub-bands of the original audio spectra, as frequency shifted by the modulators, may be selected -by appropriate filters; may be recombined either electrically or acoustically to provide a processed audio spectrum.

It is accordingly a primary object of the present invention to provide a novel photo-sensitive modulator.

It is another object of the invention to provide a novel single side band modulator utilizing photo-sensitive resistors as modulating elements.

`It is a further object of the invention to provide a system for modulating the frequency of a band of electrical signals by means of photo-sensitive devices.

It is still another object of the invention to vary the epee,

frequencies of a broad band audio spectrum by a fixed amount or by fixed increments in predetermined desired directions, by means of periodic optical shutters cooperating with photo-sensitive elements.

A further object of the invention resides in the provision of a novel polyphase signal source employing photo-sensitive resistances subjected to polyphase modulated light beams.

lt is still another object of the invention to generate a single sinusoidal voltage by rotating eccentrically mounted circular shutter discs located between elongated photo-resistors and a light source.

it is another object of the invention to provide a single side band modulator.

1t is a further object of the present invention to provide a system for shifting the frequencies of a wide band spectrum all with substantially the same deviation, by deriving from the wide spectrum duplicate wide spectra which are symmetrically phase displaced one from the other, and amplitude modulating the separate phases by means of photo-sensitive amplitude modulators in response to rotation of a light shutter, the amplitude modulation of the separate phases being in such relative phase as to cause the phasor sum of the symmetrically phased displaced spectra to rotate continuously in a given direction without amplitude Variation.

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of one speciiic embodiment thereof, especially when taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a functional block diagram of a chorus effect generator employing a frequency shift modulator in accordance with the present invention;

FIGURE 2 is a View in front elevation of a light modulating Wheel and a plurality of photo-resistor assemblies, which may be utilized in the system of FIG- URE l;

FIGURE 3 is a view in plan of a light modulating disc including phase displaced modulating tracks;

FlGURE 4 is a View in plan of a photo-resistor utilized in the practice of the present invention;

FIGURE 5 is a schematic or functional diagram of a modification of the system of FIGURE 1, which utilizes eccentrically rotating opaque discs as light modulating elements;

FIGURE 6 is a functional block diagram of a subband selection and acoustic radiating system employed in conjunction with the modulator of FIGURE 5.

Referring now more particularly to the accompanying drawings, reference numeral 10 denotes a source of an audio frequency lband or spectrum, preferably representative of music, and may be an electronic organ, or one or more of the divisions thereof. Other examples of suitable audio sources are movie sound tracks, disc or magnetic tape records, or microphones. The audio source 10 is connected in cascade with a 120 phase splitter 11 which performs the function of providing on output leads 12, 13 and 14, three audio spectra which are duplicates of that provided by the source 10, except in that the spectra are phase separated by 120. A suitable form of 120 phase splitter is illustrated and described in the above identified application of William C. Wayne, Ir.

The system of FIGURE 1 is illustrated as including only two channels, in order to simplify the exposition. It will be appreciated that the principles of the invention may be utilized in conjunction with any number of output channels, each channel involving utilization of three photo-sensitive resistors as 15, 16 and 17, in a three phase system, which are connected respectively by leads 18, 19 and 20 to the buses 12, 13` and 14, and thence via leads 21, 22 and 23 to a common lead 24. The latter connects to a band-pass filter 25 which selects a desired portion of the audio spectrum available to it. Following the practice taught in the above identified Wayne ra j. (a i;

iapplication, the band-pass iilter 2.5 may have a lband pass of one octave. The output of the band-pass filter 25 is supplied to an audio ampliiier 2d which in turn is connected in cascade with an acoustic transducer 27 such as a loudspeaker, echo chamber or the like.

Located intermediate photocells 15', 16 and 17 and a light source 30 is a rotating disc 31, rotated by a motor 32 about an axis 33. On the disc 31, and extending concentrically with the axis 33 may be located tracks capable of modulating the light deriving from the source 30. The character of the tracks is immaterial, in the sense that the tracks may be of variable density, or variable width, and in general the tracks may be arranged in accordance with techniques well known in the art of sound recording on lm. The tracks on the disc 31 are denominated 35, 36 and 37, and this set of three tracks are all of the same Afrequency but are phase displaced circumferentially by The tracks are illustrated in FIGURE 3 of the accompanying drawings, and are appropriate to radially arranged photo-resistors.

Since the tracks 35, 3d and 37 modulate the light deriving from the source 30, as that modulated light falls ou the photo-resistors 15, 16 and 17, the latter vary in resistance and accordingly amplitude modulate the signals on the leads 1S, 19 and Z0, but the amplitude modulations are in 120 phase relation because the photo-resistors are co-radial and the tracks separated in phase by 120.

it can then be shown, following teachings of the above identified Wayne application, that the band of frequencies suppiied by the audio source 10 will appear on the lead with each of its frequencies shifted 'oy an amount equal to the frequency with which each cycle of the track 35 passes any given point in space, i.e., with the frequency at which resistances 15, 16 and `1"/ are amplitude modulated. The frequencies of, the audio spectra provided by the source 1d may be increased or decreased according to the direction of rotation of the disc 31 or the interconnections sequences of the photo-resistors.

A second modulating channel may be provided, utilizing three additional photo-resistors, identified by the reference numerals 15', 16 and 17', these being modulated by means of tracks 35', 3 and 37', on the disc 31, and the outputs of the photo-resistors 15 to 17', inclusive, may be applied to a band-pass iilter 25 in cascade with an audio amplifier 26 and an acoustic transducer 27'. The tracks 15', 16 and 17' may be arranged to introduce a diiferent frequency shift than is introduced by the tracks 15., 16 and 17, and more specifically a frequency shift twice as great. In such case the band-pass filter 25 may be arranged to pass a relatively lower octave of the audio source and the band-pass filter 25' a higher octave. Suitable octaves for selections are those centered on the frequencies 277 c.p.s., 554 c.p.s., 1,108 -c.p.s., and 2,260 cps., in the case of organ music, particularly, and in such case four modulating channels may be employed which introduce frequency shifts of l, 2, 4 and 8 c.p.s. respectively, these being approximate values, and in no sense critical.

While in the system of FIGURE 1 each modulating frequency is represented on the disc 31 by three 120 phase displaced tracks, and the photo-resistors are coradial, in accordance with the system of FIGURE 2 a single track may be utilized for each modulating frequency and three 120 space displaced photo-resistive elements employed in conjunction with that track. In the system of FIGURE 2, then, the photo-resistive elements 15, 16 and 17 of FIGURE 1 may be replaced by elements 15", 16" and 1'7", in which case only one of the tracks 35, 36 and 37 need be employed as a light modulating element. 1n other respects the System of FIGURE 1 may remain identical, and accordingly it is not duplicated in the drawings.

In FIGURE 4 of the drawings is illustrated an elongated photo-resistor of the type employed in the practice of the present invention. A plate of glass or other suitable base material is employed, identified by the reference numeral 40. On the plate 40 is coated a layer of photo-resistive material 41, and two electrodes 42 and 43 which act as terminals for the photo-resistive cell, and to which may be soldered leads such as 44, 4S.

Referring now more specifically to "FIGURE 5 of the accompanying drawings, an audio source and the 120 phase splitter 11 are illustrated, these being identical with the corresponding elements of FIGURE l. In FIGURE 5, four separate modulators are illustrated, which are identified by the reference letters A, B, C and D. The several modulators are all mechanically driven by means of a belt 51. from a motor 52, and by suitably selecting the diameters of the hubs of the discs which contact belt 51, any desired speed ratios for the several discs may be provided.

Considering the modulator A as typical, three photoresistors a, b, c are provided which are arranged at 120 space relation, and with the photo-resistive elongated surfaces 41 extending toward a ycommon center, and all making the same angle with radii of the disc 5-0. In the limit the photo-resistors a, b, c may extend radially.

As the disc 50 rotates on its eccentric axis 53, each of the associated photo-resistors, a, b, c is exposed to light from a suitable source for which the disc 50 acts as a shutter, the modulation of light, as seen by the photoresistors, being sinusoidal for each of Ithe photo-resistors cz, b, c, but at 120 relative phase separations.

Since the photo-resistors a, b, c are supplied with 120 phase separated duplicate audio spectra, while their re- `sistances vary at 120 phase relation sinusoidally, the sums of the currents flowing through the photo-resistance 54, is a frequency shited duplicate of the spectrum provided by source 10.

The rates of rotation of the discs 50 with the modulators A, B, C and D may be approximately l, 2, 4 and 8 cps., respectively. The outputs of the separate modulaters may be passed through separate band-pass filters 55, 56, 57, 58, respectively, each one octave wide, and centered on the frequencies 277 c.p.s., 554 c.p.s., 1108 c.p.s. and 22li6 c.p.s., for example, the outputs of the lters being combined and amplified in a suitable amplifier 59 and acoustically transduced and radiated by a loudspeaker 60, or being separately transduced and radiated.

The sub-bands radiated by loudspeaker 60 correspond with nominally corresponding sub-bands of the original spectrum provided by source 10, but which have suffered frequency shifts of approximately 1 cps., 2 c.p.s., 4 c.p.s., and 8 c.p.s., as a function of increasing order of the subbands.

While I have described and illustrated one specific embodiment of my invention, it will be clear that variations of the details of construction which are specifically illustrated and described may be resorted to without departing from the true spirit and scope of the invention as defined in the appended claims.

What I claim is:

l. A photo-electric frequency shift modulation system, comprising photo-sensitive resistances, a source of an audio spectrum, means for splitting said audio spectrum into n duplicate spectra having phase separations 360/ n, means for applying each of said duplicate spectra in series with one of said photo-sensitive resistances, means for applying light to each of said photo-sensitive resistances, means for modulating the light as applied to the separate photo-sensitive resistances identically in frequency but in phase separation of amplitude modulations equal to 360/n, and a common load connected to all said photosensitive resistances in parallel, where n is an integer greater than two.

2. The combination according to claim l wherein said means for modulating is a separate light modulating track operatively associated with each of said photo-sensitive resistances, and motor means for moving said tracks through :re-entrant paths.

3. The combination according to claim l wherein said means for modulating is a single light modulating track for said n photo-sensitive resistances, said photo-sensitive resistances between phase separated with respect to said track -by 360/n.

y4. The combination according to claim l wherein said means for modulating is at least one opaque circular disc rotating on an eccentric axis, and operative as a light valve of variable opening for said photo-sensitive resistances.

5. A modulator for electric signal, comprising an elongated photo-resistor, means for passing an alternating current signal to be modulated through said photo-resistor, an opaque circular disc rotating on an eccentric axis, the long dimension of said photo-resistor extending both outwardly and inwardly of the outer diameter of said opaque circular disc, whereby a variable area of said photo-resistor is uncovered by said opaque disc during its Irotation, the uncovered area of said photo-sensitive resistance varying sinusoidally and in a phase determined by the angular position of said photo-sensitive resistance with respect to the circumference of said opaque disc.

6. The combination according to claim 5 wherein said signal is an audio frequency band.

7. In a photo-resistive modulator, an elongated relatively narrow photo-resistive coating having long sides and narrow ends, a pair of coated electrodes for said phottl-resistive coating, said pair of coated electrodes subsisting on opposite sides of said photo-resistive coating adjacent said long sides thereof, means for passing an a1- ternating current signal to be modulated through said photo-resistor via said electrodes, a source of light directed on said photo-sensitive coating, a light shutter located between said source of light and said photo-sensitive coating, said light shutter including an opaque portion having an edge extending across the narrow dimension of said photo-sensitive coating between said long sides, and means for moving said edge toward and away from one of said narrow ends, to expose variable areas of said photo-sensitive coating.

8. The combination according to claim 7 wherein said light shutter is a rotary circular opaque disc having a center of rotation eccentric with its circumference.

9. The combination according to claim 7 wherein said light shutter is a rotary opaque disc.

l0. A single side band carrier suppression modulation system, comprising a source of A.C. signal to be modulated, means for phase splitting said A.C. signal to form n phase separated replicas of said A.C. signal, where n is an integer greater than two, and a separate photo-sensitive modulator for amplitude modulating each of said phase separated replicas, light modulating means for arnplitude modulating light applied lto said separate photosensitive modulators in equally phase separated beams, at a common modulating frequency, and means for electrically combining the outputs of said photo-sensitive modulators.

l1, The combination according to claim 10 wherein said light modulating means includes n phase separated recorded tracks on a rotating disc, each of said recorded tracks being operatively associated with a separate one of said photo-sensitive modulators.

12. The vcombination according to claim l0 wherein said light modulating means includes a single recorded track on a rotating disc, said photo-sensitive modulators being located at n equally phase separated portions of said recorded track.

13. The combination according to claim 10 wherein said light modulating means is a rotatable opaque disc.

fl4. The combination according to claim 13 wherein said opaque disc is circular and is rotated on an axis eccentric with respect to the circumference of said disc, said photo-sensitive modulators being located at n equally separated points about the circumference of said disc.

References C11-1011 in ths le of this patent 2,159,505 UNITED STATES PATENTS 2,298,466 1,316,350 case Sept. 16, 1919 21381686 1,514,123 Bacevicz Nov. 4, 1924 2,439,392 1,886,188 Hough Nov. 1, 1932 2,503,023 1,901,400 Marrison Mar. 14, 1933 2,514,284 2,014,741 Lesa Spt. 17, 1935 2,728,835 2,043,800 xmms June 9, 1936 2,905,040 2,050,737 Schrever Aug. 11, 1936 10 2,916,796

2,155,034 Barthelemy Apr. 18, 1939 Hammond May 23, 1939 Cooley Oct. 13, 1942 Agostino et al. Sept. 18, 1945 Jones Apr. 13, 1948 Berry Apr. 4, 1950 Le Page July 4, 1950v Mueller Dec. 27, 1955 Hanert Sept. 22, 1959 Tmperman Dec. 8, 1959 

7. IN A PHOTO-RESISTIVE MODULATOR, AN ELONGATED RELATIVELY NARROW PHOTO-RESISTIVE COATING HAVING LONG SIDES AND NARROW ENDS, A PAIR OF COATED ELECTRODES FOR SAID PHOTO-RESISTIVE COATING, SAID PAIR OF COATED ELECTRODES SUBSISTING ON OPPOSITE SIDES OF SAID PHOTO-RESISTIVE COATING ADJACENT SAID LONG SIDES THEREOF, MEANS FOR PASSING AN ALTERNATING CURRENT SIGNAL TO BE MODULATED THROUGH SAID PHOTO-RESISTOR VIA SAID ELECTRODES, A SOURCE OF LIGHT DIRECTED ON SAID PHOTO-SENSITIVE COATING, A LIGHT SHUTTER LOCATED BETWEEN SAID SOURCE OF LIGHT AND SAID PHOTO-SENSITIVE COATING, SAID LIGHT SHUTTER INCLUDING AN OPAQUE PORTION HAVING AN EDGE EXTENDING ACROSS THE NARROW DIMENSION OF SAID PHOTO-SENSITIVE COATING BETWEEN SAID LONG SIDES, AND MEANS FOR MOVING SAID EDGES TOWARD AND AWAY FROM ONE OF SAID NARROW ENDS, TO EXPOSE VARIABLE AREAS OF SAID PHOTO-SENSITIVE COATING. 